The Canon 5DSr
The Canon 5DSr, Canon's DSLR with a 50 megapixel 35mm sensor, seems to be somewhat controversial amongst photographers. A recent review on Canon Rumors describes the nature of the controversy, and conveys pros and cons. The executive summary is that the camera is not cheap, has a relatively low frame rate, makes big files that are slower to process than those produced by lower resolution cameras, and amplifies mistakes in technique that you wouldn't notice with lower resolution cameras.
IMO, the review is absolutely right. But. Whether or not the qualities of the camera that the reviewer surfaces bother you is going to depend on your perspective. I bought this camera as an upgrade to a 5DMk3, although my primary camera for years now has been a Phase One medium format camera with 80 or 100 megapixel backs. Compared to these cameras which are super expensive, even more technically demanding of the photographer, with truly gigantic files, and extremely slow frame rates, shooting the 5DSr feels like a piece of cake. I find the combination of a 50mp sensor and Canon's glass a really great alternative to carrying around my medium format camera, and I have been using it extensively for natural light candids recently.
Image from 5DSr with a 200mm shot at f/2, with a full-size crop of the subject's left eye.
I shot the image above with the 5DSr and Canon's incredible 200mm f/2 prime with the aid of a monopod and image stabilization in the lens. I shot several dozen images along with this one at the same event, and was able to consistently nail critical focus and get the candid shots that I wanted. I wouldn't even have attempted to use my MF camera in this context, and none of my other cameras (Leica Q, Sony A7r2, Canon 1DXMk2) have equivalent resolution and/or optics. And you can see from the superimposed, full-resolution crop of the subject's left eye, that the amount of detail in the 5DSr's files is pretty awesome. Even if you're not making super-large prints, the extra resolution lends sharpness, and qualitatively speaking, I just like the look of these files.
My advice to folks pondering the 5DSr is think about what you're shooting first, and then map your needs to a camera. The 5DSr is great for me as a backup, although not replacement for, my medium format camera which is still a good bit sharper with dramatically better dynamic range and color rendition. IMO, it's a great camera for shooting candids and portraits, candids particularly where the extra pixels can save your ass if you got the image framed wrong or slightly missed focus and need to do sharpening and/or detail enhancement in post. I'm guessing that it's a great landscape camera. Whatever demands it places on the photographer in terms of technique is good stuff to fix, IMO, if you ever have aspirations of moving on to medium format.